1. Field of the Invention
This invention to a filter assembly for collecting material that is entrained in a gas stream such as particulate solid material or liquid in an aerosol form, and to a tubular filter element for location in a housing to collect such material.
2. Present State of the Art
Filtration of gas in a compressed gas system is generally required so that the gas is sufficiently clean for a subsequent application or to minimise adverse effects of impurities on components of the system. For example removal of compressor oil can be required to minimise chemical contamination and accumulation on valves which might lead to malfunction of the valves, and removal of particulate solid material can be required to minimise abrasion.
A known filter assembly for use in compressed gas systems is sold by Domnick Hunter Limited under the trade mark OIL-X. It comprises a housing having inlet and outlet ports for the gas stream that is to be filtered and a tubular filter element which can be located in the housing and is configured for the gas stream to flow through its wall, for example generally outwardly from the inside of the filter element to the outside. When the assembly is used to collect liquid in the gas stream (for example which is carried in the stream as an aerosol), the filter element will cause the liquid to coalesce. Coalesced liquid then drains from the filter element and collects in the housing for discharge. For such applications, the housing will include an outlet for discharge of any collected liquid.
The housing of such a filter assembly comprises a body section in which the filter element is located and in which a reservoir for any collected liquid can be provided, and a head end cap with the inlet and outlet ports for the gas stream. The filter element comprises a filter medium and first and second end fittings by which the filter medium is supported within the housing. The end fitting at the end of the filter element remote from the head end cap is connected to the end the end cap by means of a tie rod which extends through the tubular cavity within the filter element and engages the end cap by means of a thread. The extension of the tie rod through the filter element and at least partially through the end cap can disturb the flow of the gas stream through filter assembly giving rise to increased flow resistance. This therefore reduces the operating efficiency of the assembly.
The present invention provides a filter assembly in which a support extends between the filter element at or towards its end and the internal side wall of the housing at a location above the end of the housing remote from the head end cap.
Accordingly, in one aspect, the invention provides a filter assembly for collecting material that is entrained in a gas stream, which comprises a housing for a filter element. which has first and second ends with an inlet and an outlet at the first end for the gas that is to be filtered, and a support surface on its internal wall at a point towards its second end, and a tubular filter element arranged within the housing for the gas stream to flow through its wall between the inlet and the outlet, which is located in the housing by means of a support which extends between the filter element at or towards its end and the support surface on the internal side wall of the housing on which the support rests.
The housing has inlet and outlet ports for the gas stream. It can comprise a head end cap and a body section, at least one of the ports for the gas stream being provided in the head end cap. The assembly of the invention has the advantage that flow of gas through the housing head end cap and the internal cavity within the filter element (for example from the inlet to the housing for flow through the filter medium in an outward direction if the assembly operates in an in-to-out mode) is not restricted by a tie rod extending between the bottom end fitting on the filter element into the end cap. It has been found that support for the distal end of the filter element against force applied to it by pressurised gas supplied to the housing head end cap can be provided satisfactorily by a support extending to the side wall of the housing body section, the body section being connected to the end cap. The support can locate the filter element within the housing against force generally along the axis of the filter element, resulting from a pressure differential across the element.
Furthermore, the effectiveness of the seal between the filter element and the housing head end cap is not dependent on the installer of the filter element properly engaging a tie rod in the housing head end cap. By accurate control of the dimensions of the filter element and the components of the housing, the seal can be arranged to be formed reliably when the body section and the head end cap of the housing (with the filter element located inside) are connected to one another.
The present invention therefore enables the operating efficiency of a filter assembly, and the security of the seals in the assembly, to be improved compared with an assembly which uses a tie rod.
Generally, the flow of the gas stream towards and away from the assembly will be generally horizontal. The tubular filter element will generally be arranged vertically so that the housing end cap is arranged at the top of the housing, with the body section depending below it. The support for the filter element will then be located at the lower end of the element.
The filter element will generally comprise a filter medium and first and second end fittings. The support can conveniently provided on one of the end fittings. In particular, it can be preferred for the support and the end fitting to be provided as a single component, possibly as a result of being formed together for example as a single piece moulding, or as a result of being connected to one another for example mechanically, or by bonding (with or without an adhesive material). When the support is provided on one of the end fittings, it will be the bottom end fitting.
Preferably, the support extends from its end fitting towards the side wall of the housing generally transversely relative to the longitudinal axis of the filter element. For example the angle between the support and the said axis can be at least about 45xc2x0, preferably at least about 60xc2x0, more preferably at least about 75xc2x0, and possibly 90xc2x0 or more for some applications when the support will be approximately perpendicular to the axis. When the angle between the support and the axis is less than 90xc2x0, it will generally be preferred for the support to be inclined in a direction away from the housing head end cap. This has the advantage of enhancing the ability of the support to withstand force exerted by pressurised gas supplied to the housing end cap.
Preferably, the support surface faces axially in the housing towards the end of the housing from which the filter element is inserted into the housing. The support surface can be provided by a shoulder or ledge on which the filter element support can rest. The support surface can be continuous around the periphery of the housing. It can just be provided at predetermined positions appropriate for engaging the support. A discontinuous support surface can restrict rotation of the filter element relative to the housing. Accurate positioning of the support surface can ensure that the seal between the filter element and the housing head end cap is formed reliably when the body section and the head end cap of the housing are connected to one another.
Preferably, the support comprises at least three limbs which extend between the filter medium and the side wall of the housing. As a result, the filter element is supported stably within the housing, both along and transverse to its axis. The limbs will preferably be narrow when viewed along the axis of the element especially when the filter element is intended to operate in an in-to-out mode in order to minimise accumulation of any coalesced liquid at the base of the filter element. The limbs might include stiffening ribs to enhance their ability to withstand axial loads which might tend to cause them to flex or break. The length and width of the limbs might be such that the limbs appear elongate when viewed along the axis of the filter when they are longer measured transverse to the axis than they are wide measured tangentially to the axis. They might instead have the form of short tabs or tangs when they are shorter measured transverse to the axis than they are wide measured tangentially to the axis.
It can be preferred for the housing to comprise a body section and a base end cap. The support surface on which the support rests can be provided on the end cap. Preferably, the body section and the end cap are open at the interface between them so that the base end cap closes the housing at its lower end. Preferably, the support surface on which the support rests is provided at about the interface between the body section and the base end cap. For example, the support surface might be provided in the base end cap at about the interface with the body section, for example in the form of a shoulder or ledge, provided by an end surface or on an internally projecting rib or a recess.
Generally, the cross-section of the portion of the housing in which the filter element is accommodated tapers relatively little and might even have a substantially constant cross-section. Filter elements such as might be used in the assembly of the invention will generally have an appreciable transverse dimension at their base rather than being tapered to fine point and they might have a generally constant cross-section. Commonly used filter elements are cylindrical. The body section of the housing in the assembly of the invention is open in the sense that it does not taper significantly between the end of the filter element and its own end (if it extends beyond the end of the filter element) and, in particular, so that coalesced liquid that drains from the filter element does not collect in the body section before draining into the base end cap. Preferably, the body section has a substantially constant cross-section over its length and the housing includes a head end cap which closes the housing at its upper end. The constant cross-section of the body section is such that its cross-section at any two spaced apart points taken on parallel planes are similar and equal figures, apart from features by which the cross-section is specifically modified for example to provide fixation points for other components of the assembly or to provide seals to other components. The constant cross-section is such as might be formed by an extrusion process. It is an advantage of the present invention that the body section of the housing can be formed by extrusion, allowing the body section effectively to be formed continuously. The size of a housing can then be selected suit the requirements of a particular application by cutting the body section to an appropriate length. Common end caps can be used for housings with a range of capacities. Details of a housing which with a body section having a constant cross-section and separable end caps are disclosed in a copending application entitled Filter Assembly filed with the present application which claims priority from UK patent applications nos. 9726419.6 and 9815963.5 and bearing agents"" reference P11286WO. Subject matter that is disclosed in that application is incorporated in the specification of the present application by this reference.
Furthermore, the body section can be formed with formations such as ribs or grooves in its wall extending along its length. The formation can be provided with a transverse discontinuity (such as a groove when the formation is a rib) at a longitudinally extending edge thereof, by which the end cap can engage the body section. Details of a housing whose body has a constant cross-section, with a longitudinally extending internal formation and a communicating transverse formation, are disclosed in WO-A-99/30802 (which claims priority from UK patent applications nos. 9726419.6 and 9815957.7 and which has the same filing, priority and publication dates as the present application). Subject matter that is disclosed in that document is incorporated in the specification of the present application by this reference.
When the filter assembly is intended for use in applications in which liquid impurities are to be collected, the housing preferably includes an outlet at its second end for liquid entrained in the gas stream which coalesces in the filter element When the housing includes a separable base end cap, it can provide a reservoir into which coalesced liquid can drain from the filter element and which has a valved outlet for discharge of collected liquid from the housing. The reservoir within the housing can provide a xe2x80x9cquiet regionxe2x80x9d in which liquid can collect without excessive turbulence, so that re-entrainment of the liquid is minimised. A valved outlet for coalesced liquid can be provided in the base end cap. The reservoir can be made from a material that is transparent.
The filter medium will be selected according to the requirements on the assembly when in use for example in terms of the nature and quantity of the impurity (for example as to whether it comprises liquid impurity or solid impurity or both) in the gas stream, the degree of filtration required of the medium, the pressure to which the assembly is exposed when in use. When the impurity to be collected includes liquid (which will generally be present as an aerosol for example of compressor oil), the filter medium will preferably be capable of causing liquid droplets to coalesce. Materials suitable for use in a coalescing filter element are known, including those sold by Domnick Hunter Limited under the trade mark OIL-X. Suitable materials include borosilicate and other glass fibres, activated carbon materials, activated silica materials and so on.
Preferably, the housing comprises a head end cap and a body section which can be separated to allow access to the interior of the housing, the support for locating the filter element being provided on the end of the filter element that is remote from the head end cap. When the head end cap and the body section are separated, a filter element within the housing can be inspected and replaced if necessary.
It is preferred that the assembly includes a flow conduit which can be fitted into the head end cap, with one end sealed to a port in the end cap, for directing the flow of gas between a port in the head end cap and the filter medium, especially the tubular cavity within the filter element defined by the filter medium The connection between the flow conduit and the head end cap might be temporary when separation of the end cap and the flow conduit is required or it might be substantially permanent The use of a flow conduit which is fitted into the head end cap has the advantage that the flow conduit can be made with a configuration that is not restricted by having to be formed as an integral part of the end cap. For example, when the axes of the openings at the opposite ends of the conduit are not aligned, the flow path between the openings can be configured to present a continuous smooth flow path to the gas stream flowing along it between the first and second conduit openings. The smooth flow path can be constructed to reduce restriction of the flow of the gas stream compared for example with a flow conduit which presents a discontinuous flow path which is sharply angled or contains steps or other obstructions. The flow conduit can be made with additional features during its manufacture. For example, a port might be formed in it for connection to means for indicating the pressure within the conduit. A tang might be formed on the flow conduit which can be received in a recess in the housing when the flow conduit is properly located within the housing end cap. This can provide an indication that the flow conduit is properly located, for example by visual inspection or as a result of the tang being resiliently deformable and being received in the recess with a snap fit. The flow conduit can be located in its appropriate position within the end cap by means of interengaging ribs on the flow conduit and the end cap respectively. Details of a filter assembly with a separable flow conduit which is located against a port in a housing by sliding it generally transversely relative to the direction of flow of gas through the port are disclosed in WO-A-99/30798 (which claims priority from UK patent applications nos. 9726415.4 and 9815961.9 and which has the same filing, priority and publication dates as the present application). Details of a filter assembly in which a flow conduit is located in an end cap of a housing, which also includes a body section for receiving the filter element, are disclosed in WO-A-99/30799 (which claims priority from UK patent applications nos. 9726415.4 and 9815959.3 and which has the same filing, priority and publication dates as the present application). Subject matter disclosed in those documents is incorporated in the specification of the present application by this reference.
The filter element is located largely within the body section of the housing. Generally, the correction to the filter element for the flow of gases is made at about the interface between the body section and the housing head end cap. However, the filter element might protrude beyond the end of the body section or the body section might extend beyond the end of the filter element. The housing body section and the or each end cap should be capable of being connected to one another with sufficient security to withstand internal pressures to which the assembly is subjected when in use. Examples of appropriate connections include threaded and bayonet type connections. Preferably, the assembly includes means for indicating when the end cap and the body section are connected to one another sufficiently securely to withstand the internal pressures. This can have the advantage of also indicating that the filter element is properly and sealingly connected to the conduit in the end cap through which gas flows between the end cap and the inside of the filter element. The indicating means can also indicate that a flow conduit that is separable from the housing head end cap is appropriately located in its end cap, for example when the flow conduit engages the body section (directly or indirectly) and it is through the action of the body section on the flow conduit that the flow conduit is forced into the housing end cap. The indication can be visual, for example involving the appearance of a marking in the housing or the flow conduit. The indication can be sensed in other ways, for example by feeling engagement of a resilient member in a recess. For example, one of the flow conduit and the housing can bear a resiliently deformable tang and the other of the flow conduit and the housing can have a recess formed in it in which the tang is received when the flow conduit is properly located within the housing end cap. In a preferred embodiment, the tang is provided on the flow conduit and the recess is provided in the housing end cap.
Preferably, one or both of the end fittings for the filter element are made from a polymeric material such as a polyolefin, a polyamide, or a polyester. The polymeric material can be reinforced for example by fibres. The use of a polymeric material for the end fittings has the advantage that it can conveniently be formed by a moulding process, with the flow conduit or the support for the filter element according to the design of the filter element for any particular application.
It will often be preferred for one, especially both, of the body section and the head end cap of the housing to be formed from a metallic material such as a steel or an aluminium alloy, in particular to enable the housing to withstand the internal pressures to which it is exposed when in use. The end cap will then often be made from a casting process. Polymeric materials can be appropriate for many applications, for example when the filter assembly is only to be exposed to moderate pressures in use or has a small size.
Preferably, the head end cap has at least three ports which are to provide between them the inlet and outlet for the gas that is to be filtered. The provision of at least three ports can enable selection of the relative orientation of the inlet and the outlet by selection of the ports in the end cap that are to provide the inlet and the outlet respectively. The assembly can include an adaptor block having formations in it by which a connection can be made to another component (such as a closure cap for sealing the port against flow of gas, a conduit for the flow of gas to or from the filter assembly, or a connector by which the housing end cap can be connected to a similar port on the housing end cap of another filter assembly), the block and the end cap being capable of being sealingly connected to one another with the block located adjacent to one of the ports of the end cap to provide for flow of the gas stream between the said other component and the said port.
Generally, the flow conduit between the internal cavity in the filter element and a port in the head of the housing (whether or not it is separable from the housing head) will provide a path for the gas stream to flow between the inlet in the housing end cap and the tubular cavity within the filter element for the gas to flow outwardly through the filter medium provided in wall of the element so that the filter element functions in an in-to-out mode. Alternative arrangements are envisaged. For example, the flow conduit can provide a path for the gas stream to flow between the tubular cavity within the filter element and the outlet in the housing end cap after the gas has flowed inwardly through the filter medium, so that the filter element functions in an out-to-in mode.
The filter element comprises a tubular body of filter medium and top and bottom end fittings by which the filter medium is supported within the housing. The flow conduit or the support or both can be provided as part of one of the end fittings of the filter element, especially when the end fitting (including the flow conduit or the support) is formed by a moulding operation.
In another aspect, the invention provides a tubular filter element for location in a housing for collecting material that is entrained in a gas stream by passing the gas stream through the wall of the element which comprises a filter medium, the element comprising first and second end fittings by which connections are formed between the filter element and a housing in which it is located in use, one of the end fittings including a support which extends between the filter element and the internal side wall of the housing to restrict the filter element against movement within the housing in a direction along the axis of the filter element.
Preferably, the filter element can be removed from the housing with the support as a one-piece assembly. For example, the support and the end fitting of the filter element can be incorporated into the element as a single component, for example by being manufactured as a single piece (such as by moulding) or by manufacture as a number of pieces which are fastened to one another, for example mechanically or by bonding (with or without an adhesive material).
Preferably, the filter element includes a flow conduit for directing the flow of gas between the tubular cavity within the element (defined by the filter medium) and a port in the head of a housing, the flow conduit being separable from the end cap. Preferably, the filter element can be removed from the housing with the flow conduit as a one-piece assembly. For example, the flow conduit and the end fitting of the filter element can be incorporated into the element as a single component, for example by being manufactured as a single piece (such as by moulding) or by manufacture as a number of pieces which are fastened to one another, for example mechanically or by bonding (with or without an adhesive material).
Preferably, the top end fitting bears a tang which can be deformed resiliently during formation of a connection between the filter element and a housing, and which, when the connection is formed, can be received in a recess in the housing which allows the configuration of the tang to be restored at least partially towards its undeformed configuration. Details of the location of a deformable tang in a recess to indicate proper connection of components of a filter assembly are disclosed in the copending application entitled Filter Assembly filed with the present application which claims priority from UK patent applications nos. 9726418.8 and 9815955.1 and bearing agents"" reference P11284WO. Subject matter disclosed in that application is incorporated in the specification of the present application by this reference.